Channel estimation is an important aspect of wireless communication systems, since the performance of such systems is directly related to the accuracy of the channel estimation. The channel estimation should be as robust as possible under any wireless channel conditions. However, conventional channel estimation is usually poor under a low signal-to-noise ratio (SNR) channel condition.
FIG. 1 is a block diagram of a transmitter 110 and a receiver 130 implementing a conventional channel estimation method. At the transmitter 110, data symbols 112 and pilot symbols 114 are multiplexed by a multiplexer 116. The multiplexing of the pilot and data symbols may be performed in a time domain, a frequency domain, or a code domain. The multiplexed data and pilot symbols 118 are modulated by a modulator 120 and the modulated data and pilot symbols 122 are transmitted via a channel. At the receiver 130, a demultiplexer 134 separates the data symbols 136 and pilot symbols 138 from the received signal 132. A channel estimator 140 performs channel estimation using the received pilot symbols 138. Interpolation in a time domain, in a frequency domain, or both between pilot symbols may be performed. A detector/demodulator 144 detects and demodulates the data symbols based on the channel estimate 142.
Conventional channel estimation schemes are vulnerable to high noise power levels, which results in poor receiver performance and high detection errors. Since the conventional channel estimation is performed by using non-localized pilots, such as pseudo-noise (PN) sequences, it is not possible to apply time-frequency domain de-noising techniques.
Therefore, it would be desirable to provide a method and apparatus for channel estimation using time-frequency localized pilots and de-noising techniques.